Linear polyolefins made using a mono-functional initiator containing a single “exo-olefin”, “di-substituted” olefin, or “methyl vinylidene group,” end group are useful precursors for the preparation of polymers containing specific functional end groups. Polymers made using multi-functional initiators would have multiple exo-olefinic end groups. Polymers containing specific end groups are useful as lubricating oil additives. One example of a functionalized polymer containing hetero atoms is polyisobutenylsuccinic anhydride. Functional end groups may also be desirable for making polymers with potential for further reactions.
Conventional ionic polymerizations can be anionic or cationic. Anionic polymerizations proceed, in the presence of a base, through carbanions and favor monomers having electron withdrawing groups. Cationic polymerizations proceed, in the presence of an acid, through a carbocation, also called a carbenium ion, and favor monomers that have electron releasing groups.
Similarly to the conventional polymerization systems, living polymerization systems may be either anionic or cationic. The difference between conventional polymerizations and living polymerizations is that an ideal living polymerization proceeds in the absence of chain transfer and chain termination. Living polymerization systems are of great commercial importance because the degree of polymerization may be controlled by controlling the feed ratio of monomer to initiator and sequential addition of two or more different monomers affords the ability to produce block copolymers. Polymerization continues until the monomer is exhausted, but the polymers retain their ability to add additional monomers any time in the future. A number of such systems are well known in the art.
A further development is the cationic quasi-living polymerization systems using conventional monomers. Quasi-living polymerization requires certain restrictive conditions, for example anhydrous reagents. Cationic quasi-living polymerizations differ from truly living polymerizations in that, although the rate of chain transfer approaches zero, chain termination is present but reversible. One important example of a cationic quasi-living polymerization is the cationic quasi-living polymerization of isobutylene.
Typically, cationic quasi-living polymerizations of isobutylene yield narrow molecular weight distribution and one major polymer product containing the 2-chloro-2-methylpropyl end group, also referred to as the “tert-chloride” end group. Under certain conditions minor amounts of olefinic isomers may also be produced.
On the other hand, there are two major olefinic isomers produced during conventional polymerization of isobutylene with BF3, for example, the highly reactive exo-olefin isomer and the relatively unreactive 2-methyl-1-propenyl isomer, also referred to as the “tri-substituted” isomer or “endo olefin” isomer. Furthermore, conventional polymerizations of isobutylene yield polymers with broad molecular weight distributions or polydispersity indices.
Exclusive production of the exo-olefin isomer has not been previously achieved under conventional polymerization conditions for isobutylene.
There are two established methods for producing polyisobutylene containing only the exo-olefin end group. One method involves chemical dehydrohalogenation of tert-chloride terminated polyisobutylene using potassium tert-butoxide in a post polymerization reaction (U.S. Pat. No. 4,342,849). The other method involves in situ quenching of quasi-living isobutylene with methallyltrimethylsilane, which converts an active, living carbenium ion to the exo-olefin end group. (M. Roth and H. Mayr, Macromolecules, 29, 6104, 1996)
Polyisobutylene polymers containing more than one exo-olefin end group may be prepared using the above methods by the use of a multi-functional initiator.
The preparation of polyolefins, including polyisobutylene polymers, is well known in the art. A number of patents have discussed processes for making polyisobutylene polymers containing exo-olefin end groups, but none using quenching a cationic quasi-living polymerization system with a hindered secondary or tertiary amine.
European Patent No. 341012 discloses a method for producing polymers with narrow molecular weight distribution, where the ratio of the weight average molecular weight, M(w), to the number average molecular weight, M(n), approaches 1.
U.S. Pat. No. 4,152,499 discloses isobutene polymers having a mean degree of polymerization from 10 to 100 and where the proportion of theoretically possible terminal double bonds is greater than in products prepared using aluminum trichloride. The patent also discloses the method of making the isobutene polymers using boron trifluoride as the initiator.
U.S. Pat. No. 4,342,849 discloses the synthesis of polyisobutylene carrying either unsaturation or hydroxyl groups at both ends, in the case of a linear polymer, or at all ends in the case of a star polymer. The method involves the steps of refluxing a solution of telechelic di-halogen polyisobutylene, adding a solution strong base such as potassium t-butoxide and stirring to form the telechelic di-olefin polyisobutylene.
U.S. Pat. No. 4,393,199 discloses a method for carrying out cationic polymerization with molecular weight control in which a pre-initiator and a catalyst effective for cationic polymerization are mixed with a monomer. The resulting living polymer is then treated as desired.
U.S. Pat. No. 4,758,631 discloses a method of preparing allyl-terminated polyisobutylene by allylation with allyltrimethylsilane of tertiary chloro-capped polyisobutylene by electrophilic substitution. The synthesis begins with the boron trichloride catalyzed mono- or oligo-tertiary chloride “inifer” initiated polymerization of isobutylene, followed in the same reaction vessel by the addition of hexane, allyltrimethylsilane and titanium tetrachloride.
U.S. Pat. Nos. 4,910,321 and 5,122,572 disclose a catalyst composed of a complex of an organic acid or its ester and a Lewis acid, preferably boron trichloride that can add olefin monomers to increase the molecular weight of the complex from as low as 200 to in excess of a million. The patents also disclose polymers of different molecular weights having useful end groups such as halogens and specifically chloride, allyl, acryl or methacryl, acetate or formate.
U.S. Pat. Nos. 4,929,683 and 5,066,730 disclose a catalyst composed of a complex of an organic ether and a Lewis acid, preferably boron trichloride that can add olefin monomers to increase the molecular weight of the complex from as low as 200 to in excess of a million. The patents also disclose polymers of different molecular weights having useful end groups such as halogens and specifically chloride, allyl, acryl or methacryl, acetate or formate.
U.S. Pat. No. 5,219,948 discloses a method for preparing elastomeric polymers comprising alpha-olefins or conjugated alkadienes by cationic polymerization in the presence of titanium tetrachloride and an electron pair donor selected from pyridine or a non-hindered alkylpyridine. The polymers have very narrow, mono-modal molecular weight distribution.
U.S. Pat. No. 5,336,745 discloses a method for the direct synthesis of polymeric materials functionalized with desirable nitrogen-containing functional groups such as terminal azido, cyano, carbonylamino or thiocarbonylamino groups. Polymerization and functionalization occur in a substantially simultaneous manner.
U.S. Pat. No. 5,428,111 discloses a process for the living polymerization of aromatic, preferably styrenic monomers initiated from a living polyolefin, particularly polyisobutylene, chain end for making block copolymers having polyolefin mid-blocks and styrenic end-blocks.
U.S. Pat. No. 5,448,000 discloses a one-pot method of preparing sulfonic acid-terminated polyisobutylene by sulfonation with acetyl sulfate of a living polyisobutylene in a single step. The method involves “inifer” initiated carbocationic polymerization with Lewis acid to form the polymer followed by the sulfonation.
U.S. Pat. Nos. 5,637,647 and 5,677,386 disclose the capping of a living polymer with one or more capping compounds comprising non-polymerizable monomer selected from a group consisting of substituted or unsubstituted diphenyl alkylene, methoxystyrene, trans-stilbene, 1-isopropenylnaphthalene and 2,4-dimethyl styrene.
U.S. patent application Ser. No. 10/433,439, Publication No. 2004/0015029 A1, discloses a process for the preparation of polyisobutylenes in which at least 60 percent of the polymer chains have at least one olefinically unsaturated terminal group, by cationic polymerization of isobutene or isobutene-containing monomer mixtures in the condensed phase and in the presence of an initiator system.
U.S. patent application Ser. No. 10/600,898, Publication No. 2004/0260033 A1, discloses the method for manufacturing and producing monodisperse telechelic polymers through cationic polymerization of suitable monomer under living polymerization conditions and quenching the polymerization with an N-substituted pyrrole. The functionalized polymers containing N-substituted pyrroles may be employed as fuel additives and/or lubricating oil additives.
PCT International Application No. PCT/EP/05472, International Publication No. WO99/09074, discloses a process for functionalizing polymers prepared by cationic polymerization wherein a living carbocationic polymerization system is reacted with one or more aromatic ring systems, and the use of substituted or unsubstituted reaction products of said process in lubricating oil or fuel compositions and additive concentrates, for example as dispersants, detergents or antioxidant additives or VI improvers.
β-Proton elimination by Free Bases in the Living cationic Polymerization of Isobutylene, by Young Cheol Bae and Rudolf Faust, Macromolecules, Volume 30, 7341-7344 (1997). The authors investigated β-proton elimination from quasi-living polyisobutylene, after observing exo-olefin formation in the presence of 2,6-di-tert-butylpyridine (DTBP) of low purity. They ascribed elimination to the presence of a sterically hindered cyclic imine base present in the DTBP in a concentration of 6×10−6 moles per liter. They simulated this impurity using 2-tert-butylpyridine (TBP) and discovered that the latter, when added to the reactor at the start of the polymerization (i.e., in the presence of monomer) resulted in about 65 percent elimination after 3 hours of reaction time to produce exclusively exo-olefin. When the extent of elimination had reached 20 percent or higher, significant coupling was observed from both 1H NMR and GPC analyses. Bae and Faust clearly considered that elimination by sterically hindered bases, such as TBP, was undesirable and should be avoided. The first paragraph of the paper was summarized as follows: “Finally, strong bases may also eliminate β-protons, which should be avoided.” Later, they refer to the cyclic imine base impurity in DTBP as “the culprit.” Finally, they summarized the entire paper by saying that the elimination process should be avoided for polymer preparation purposes, although it might facilitate the measurement of kinetic rate constants: “While β-proton elimination should be avoided for the synthesis of well-defined macromolecules, if diffusion control of this process can be shown, it may provide a novel method of establishing the concentration of active centers, from which absolute propagation rate constants could be calculated.”